The present application relates generally to polymerizable alkene-sulfide compounds and to a method of preparing such compounds from acetylenic compounds. In particular, the invention is directed to photosensitive polymerizable alkene-sulfide compounds that can be used to form polymeric materials having a refractive index greater than 1.60 that can be used to make optical elements and devices useful in optical telecommunications.
The refractive index (n) of a polymer is defined as the ratio of the velocity of light in a vacuum (c) to the velocity of light in the polymer material (v) at a certain wavelength (xcex). According to the Maxwell equation (1), the refractive index is the ratio of magnetic field strength (H) with electric field strength (E), which increases with the polarizability ("khgr") of the molecules.                     n        =                              H            E                    =                                                    1                +                                  4                  ⁢                                      xe2x80x83                                    ⁢                  π                  ⁢                                      xe2x80x83                                    ⁢                  χ                                                      ≅                          1              +                              2                ⁢                                  xe2x80x83                                ⁢                π                ⁢                                  xe2x80x83                                ⁢                χ                                                                        (        1        )            
For a covalent bonded polymer system, the refractive index can be treated as the sum of the bond refractions that make up the repeat unit of the polymer chain [K. G. Denbigh, Trans. Faraday Soc. 36 (1940), 936]. Thus, a polymer structure constructed from polarizable larger size building blocks (or elements) such as Br, I, S, Se, phenyl groups, etc. often have a higher refractive index. In contrast, the less polarizable chemical bonds in a fluorinated polymer depress the refractive index.
Most of the high refractive index compounds from inorganic or organic/inorganic hybrid materials are chemically bonded by ionic interaction. The poor hydrolytic stability caused by their high dipole moment combined with their higher optical loss limits the application of many high refractive index materials in the telecommunication industry. In comparison with traditional inorganic glass and ceramic materials, polymer materials, which are covalently bonded macromolecules, exhibit unique mechanical, processing and optical properties. High refractive index. (xe2x80x9cRIxe2x80x9d) polymer materials (RI greater than 1.60 at 632 nm) have been used as plastic lenses to replace the heavy inorganic glass lens in our daily life. In the optical communication industry, high refractive index polymer materials have been applied in specialty optical fiber; for example, erbium doped amplify fiber (EDAF) as an outer cladding layer to strip the cladding modes. In tunable polymer Bragg grating filter devices, an alternating high and low index periodic structure is the key to achieving a thermally tunable grating for wavelength selective switches.
The optical switch is one of the most important components in the optical network. Among the different designs of optical switches are the thermal optical, electro-mechanical, electro-optical, and liquid crystal switches. The liquid crystal optical switch is a niche device known for its fast switch time and possibly lower fabrication processing cost. In the design of a high efficient liquid crystal switch, the polarizing splitter and combiner require a high refractive index waveguide (1.68-1.72 at 1550 nm) to match the refractive index of the liquid crystal molecules which normally contain ridged rod moieties of high refractive index phenyl groups. Many such materials contain urethane or epoxy groups that are used for crosslinking the polymers forming the rigid rods. Materials containing urethane or epoxy groups are not suitable for optical coatings or for use in optical waveguide applications because of high optical losses due to the presence NH or OH groups. Much more desirable are materials that do not contain such NH and OH groups.
Thiol-ene chemistry, the reaction between an alkene compound and a thiol compound, has been extensively used for polymer modification and rubber crosslinking. [Kobayashi et al., J. Makromol. Chem. Vol. 3 (Elsevier, London 1993), 2525-2533]. The mechanism of thiol-ene is well known as a radical addition reaction. The thiol-ene reaction may be viewed as ultimately being the addition of a xe2x80x94SH moiety across an alkene double bond, resulting in a saturated product. Less well known is the analogous reaction between an alkyne (an acetylenic compound) and a thiol (that is, xe2x80x9cthiol-ynexe2x80x9d chemistry). Dithio compounds and (phenyl)-diynes have been reported to yield polysulfide containing polymers that are insoluble in any organic solvent. [Oskar Nuyken et al., xe2x80x9cNovel Sulfur-containing telechelices with alternating aliphatic-aromatic structure unitsxe2x80x9d, Polymer Bulletin 19 (1998), 371]. Such compounds, which are solids, are unsuitable for use in telecommunication applications because of their inability to be coated onto substrates. In order to be used as a coating material such compounds must either be a liquid of suitable viscosity or soluble in a selected solvent. Under special conditions such as UV radiation, a soluble polymer has been reported from the reaction of a dithiol with a diallene compound (I) [HCxe2x95x90Cxe2x95x90CHxe2x80x94Oxe2x80x94C6H4xe2x80x94Oxe2x80x94CHxe2x89xa1Cxe2x95x90CH2 (I)⇄HCxe2x89xa1Cxe2x80x94CH2xe2x80x94Oxe2x80x94C6H4xe2x80x94Oxe2x80x94CH2xe2x80x94Cxe2x89xa1CH (II)] formed from the dialkyne (II) to yield Anti-Markovnikov products. [E. Sato et al., xe2x80x9cPolyaddition of diallenes: radical polyaddition of dithiols to 1,4-bis(allenyloxy)benzenexe2x80x9d, Macromolecules 26, No. 19, (1998), 5185-5186 and 5187-5191.] However, overall, the chemical literature does not disclose generally useful methods for reacting alkynes and thiols to prepare compounds having polymerizable double bonds which can be used as-is to coat substrates for telecommunications applications, or which are soluble in selected solvents so that they can be used for such purposes.
The preparation of reactive alkenes having sulfur atoms attached to at least one of the carbon atoms of the double bond would be highly desirous for use in the preparation of polymeric materials having a high refractive index and low losses.
The invention is directed to the preparation of vinyl sulfide compounds of general formula xe2x80x94(xe2x80x94R1xe2x80x94Sxe2x80x94R4Cxe2x95x90CR5xe2x80x94R3xe2x80x94Sxe2x80x94)nxe2x80x94(xe2x80x94R2xe2x80x94Sxe2x80x94R4Cxe2x95x90CR5xe2x80x94R3xe2x80x94Sxe2x80x94)m formed by the Markovnikov (xe2x80x9cMKxe2x80x9d) or anti-Markovnikov (xe2x80x9cAMKxe2x80x9d) addition of a dithiol compound of general formula HSxe2x80x94R1xe2x80x94SH with an acetylenic compound of general formula R4(or R5)Cxe2x89xa1Cxe2x80x94R3xe2x80x94Sxe2x80x94R2xe2x80x94Sxe2x80x94R3xe2x80x94Cxe2x89xa1CR4(or R5); where:
(1) R1 and R2, independently of each other and of R3, are an alkyl group, an aryl group, a dialkyl sulfide group (-alkyl-S-alkyl-), a diaryl sulfide group (-aryl-S-aryl-) or a mixed alkyl-aryl sulfide group (-alkyl-S-aryl-), the R1 and R2 alkyl groups being C1-C6 alkyl groups selected independently of each other, and the aryl groups being phenyl and alkyl, deuterium or halogen substituted phenyl groups;
(2) R3 is methylene (xe2x80x94CH2xe2x80x94) or a mono-/di-substituted methylene group wherein said substituent(s) is/are, independently, C1-C6 alkyl groups;
(3) R4 and R5, independently of each other, are H or CH3; and
(4) m and n, independently of each other, are integers in the range of 1-1000, and preferably in the range of 1-100.
The invention is further directed to a method of preparing compounds of general formula xe2x80x94(xe2x80x94R1xe2x80x94Sxe2x80x94R4Cxe2x95x90CR5xe2x80x94R3xe2x80x94Sxe2x80x94)nxe2x80x94(xe2x80x94R2xe2x80x94Sxe2x80x94R4Cxe2x95x90CR5xe2x80x94R3xe2x80x94Sxe2x80x94)m.
In addition, the invention is directed to monomeric compounds of general formula R4(or R5)Cxe2x89xa1Cxe2x80x94R3xe2x80x94Sxe2x80x94R2xe2x80x94Sxe2x80x94R3xe2x80x94Cxe2x89xa1C R4(or r5) and to a method of preparing such compounds by the reaction of a halogenated acetylenic compound of general formula R4(or R5)Cxe2x89xa1Cxe2x80x94R3X with a dithiol compound of general formula HSxe2x80x94R2xe2x80x94SH, where:
(1) R2 is an alkyl group, an aryl group, a dialkyl sulfide group (-alkyl-S-alkyl-), an aryl sulfide group (-aryl-S-aryl-), or a mixed alkyl-aryl sulfide group (-alkyl-S-aryl-); the alkyl groups being C1-C6 alkyl groups selected independently of each and the aryl groups being phenyl and alkyl, deuterium or halogen substituted phenyl groups;
(2) R3 is a methylene (xe2x80x94CH2xe2x80x94) or a mono-/di-substituted methylene group wherein said substituent(s) is/are, independently, C1-C6 alkyl groups; and
(3) R4 and R5, independently of each other, are H or CH3.
The invention is also directed to polymeric materials obtained by (a) the homopolymerization of compounds of compounds of general formula xe2x80x94(xe2x80x94R1xe2x80x94Sxe2x80x94R4Cxe2x95x90CR5xe2x80x94R3xe2x80x94Sxe2x80x94)nxe2x80x94(xe2x80x94R2xe2x80x94Sxe2x80x94R4Cxe2x95x90CR5xe2x80x94R3xe2x80x94Sxe2x80x94)m and (b) the copolymerization of compounds of general formula xe2x80x94(xe2x80x94R1xe2x80x94Sxe2x80x94R4Cxe2x95x90CR5xe2x80x94R3xe2x80x94Sxe2x80x94)nxe2x80x94(xe2x80x94R2xe2x80x94Sxe2x80x94R4Cxe2x95x90CR5xe2x80x94R3xe2x80x94Sxe2x80x94)m with monomers and oligomers containing polymerizable xe2x80x94Cxe2x95x90Cxe2x80x94 groups, including acrylate and methacrylate monomers and oligomers.
It is to be understood that both the foregoing general description and the following detailed description present embodiments of the invention, and are intended to provide an overview or framework for understanding the nature and character of the invention as it is claimed.